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Metal Forming Application

Introduction

The first documented publications to thrust LS-DYNA® onto the international stage were two papers [1,2], published in International Conference of FE-Simulation of 3-D Sheet Metal Forming Processes in Automotive Industry, May, 1991, Zurich, Switzerland:

  1. Improving Standard Shell Elements Friction Models and Contact Algorithms for the Efficient Solution of Sheet Metal Forming Problems with LS-DYNA3D, by J.O. Hallquist, D.W. Stillman, K. Schweizerhof and K. Weimar.
  2. Explicit Time Integration and Contact Simulations for Thin Sheet Metalforming, by K. Schweizerhof and J. O. Hallquist;

The content of the two papers are self-explanatory from the paper titles.

The year of 1991 proved to be a very significant and productive year for LS-DYNA in forming simulation, which also included three more publications in VDI BERICHTE NR. 894, 1991 [3,4,5]. The papers discussed detailed evaluation and application of LS-DYNA in three-dimensional sheet metal forming in various small laboratory parts and in full-scaled industrial stamping concerns at Volvo [4] and Mercedes-Benz [5]. Considering the time they were published, the actual work must have been done at least several years earlier. There would be many years gone by before other specialized stamping simulation software became commercially available.

The year of 1991 was also the beginning of a paradigm shift for the entire tool and die industry worldwide. Stamping die development using hand-made plaster models for as long as the industrial existed would be quickly replaced by the CAD and CAE technology that use software such as LS-DYNA. Within 10 years, hand-developments of stamping dies with plaster model would all but disappear from the tool and die industry in North America. Soft dies that used to prove various draw die development concepts are no more. Traditional method of ‘heat & beat’ was replaced by the cutting edge CAE simulation technology. Along with the shift, a whole new profession of stamping simulation engineers was born, some of them from skilled, traditional die shop workers. There was a huge explosion in productivity and efficiency in the stamping manufacturing engineering.

From day one, the development of LS-DYNA has been intensively focused on accuracy and functionality. This development philosophy has allowed LS-DYNA to become a premier stamping simulation software. LS-DYNA is the software of choice for the most advanced and complex stamping processes calculations. The accuracy of LS-DYNA is well documented, through international benchmarks in sheet metal forming, such as the NUMISHEET series of conferences. Because of this focus, LS-DYNA has passed many independent benchmarks and evaluations by its users against experimental measurements and was the first commercial software to be intensively applied in the virtual environment to drive industrial stamping manufacturing engineering and production. It has become an integrated critical path in the advance manufacturing engineer process in majority of OEMs and their suppliers. Today’s LS-DYNA, with its powerful MPP technology, can take on the most challenging industrial stamping problems that no other software can do, such as computing with ease detailed stampings with 10 million plus shell or solid elements both explicitly and implicitly, with incredible speed. At LSTC, we form the impossible.

As much as we would like to emphasize how powerful LS-DYNA is, the importance of human-ware is undoubtedly just as critical. Experiences has proven, extraordinary success is afforded to those engineers who take the time to understand the capabilities of LS-DYNA, to study in details its results, and to apply in every aspects of stamping manufacturing engineering.

  • Reference:
  1. J.O. Hallquist, D.W. Stillman, K. Schweizerhof and K. Weimar: Improving Standard Shell Elements Friction Models and Contact Algorithms for the Efficient Solution of Sheet Metal Forming Problems with LS-DYNA3D, International Conference of FE-Simulation of 3-D Sheet Metal Forming Processes in Automotive Industry, May, 1991, Zurich, Switzerland.
  2. K. Schweizerhof and J. O. Hallquist: Explicit Time Integration and Contact Simulations for Thin Sheet Metalforming, International Conference of FE-Simulation of 3-D Sheet Metal Forming Processes in Automotive Industry, May, 1991, Zurich, Switzerland.
  3. P.C. Galbraith, M.J. Finn, S.R. MacEwen, A.R. Carr, K.M. Gatenby, T.L. Lin, G.A. Clifford, J.O. Hallquist and D. Stillman: Evaluation of an LS-DYNA3D Model for Deep Drawing of Aluminum Sheet, VDI BERICHTE NR. 894, 1991.
  4. K. Mattiasson, L. Bernsprang, A. Honecker, E. Schedin, T. Hammam , and A. Melander: On the Use of Explicit Time Integration in Finite Element Simulation of Industrial Sheet Forming Processes, VDI BERICHTE NR. 894, 1991.
  5. M. Grober and K. Gruber: Numerical Simulation of Sheet Metal Forming of Large Car Body Components, VDI BERICHTE NR. 894, 1991.

Application Fields

LS-DYNA is the most versatile software available commercially, owing to its development strategy of one scalable code that integrates multi-physics, multi-stage, and multi-scale capabilities. Application of LS-DYNA in stamping manufacturing engineering is fully process dependent, limited only by the imaginations of its users, and has proven to be applicable (but not limited) in the following areas:

  • Gravity loading (implicit)
  • Binder closing/setting (implicit & explicit)
  • Forming (thin, thick shells and solids)
  • Flanging (think shell & solids, implicit & explicit)
  • Hemming (press & roller)
  • Springback (free standing or on fixture nets)
  • Springback compensation of stamping die and line dies
  • Assembly simulation (clamping forces, permanent set, springback, etc.)
  • Stoning for surface defects of exterior panels
  • Dynamic panel transfer (transfer press line)
  • Panel dropping (onto fixture) simulation
  • Stamping optimization (draw beads, material properties & tool geometry, etc.)
  • Various static & dynamic loading of structures
  • Denting and snap-through simulation
  • One-step stamping initialization for subsequent process (crash simulation, etc.)
  • Stamping scrap shedding process
  • Tube-bending/Hydro-forming
  • Hot/warm stamping & superplastic forming
  • Magnetic metal forming

Most of the applications also feature 2-D as well as 3-D elements.

Rapid Advancement

At LSTC, new features related to sheet forming are rapidly added, intensified and completely driven by customer demand. This allows us to meet the specific needs of new stamping applications, whether it is a new material or a new process, and a growing customer base.

Some of the recently developed features include:

  • Modified Yoshida kinematic non-linear hardening models, for Ultra-High Strength Steel (UHSS) & Aluminum stamping and springback simulation, with Hill’s and Barlat’s yield criteria
  • Stamping die compensation for springback (in production use since early 2006) with new features developed:
    • - Global, local, iterative, on draw die, trimming die & flanging die
      - Accelerated iterative compensation
  • New features in implicit/explicit development and application
    • - Gravity, binder closing, flanging simulation
      - Contact-based scrap fall simulation
  • Stoning simulation for surface defects of exterior surface panels
  • Directional and pressure sensitive friction model
  • Failure prediction with Formability Index (F.I.) for forming limits with non-linear strain path
  • One-step stamping initialization for crash/durability
  • Assembly simulation (clamping forces, permanent set, springback, etc.)
  • Stoning for surface defects of exterior panels
  • Dynamic panel transfer (transfer press line)
  • Panel dropping (onto fixture) simulation
  • Stamping optimization (draw beads, material properties & tool geometry, etc.)
  • Various static & dynamic loading of structures
  • Denting and snap-through simulation
  • One-step stamping initialization for subsequent process (crash simulation, etc.)

Mutual Benefits

LS-DYNA benefits by working with the industry’s best and brightest. The close working relationship has allowed LS-DYNA to stay in the forefront of the forming technology. Our customers also benefit from a more capable software that can handle the most demanding, challenging and state-of-art manufacturing application. For the past two decades, LSTC has been the only FEA software company selected to participate in all major industrial/government consortium projects in the United States, with some of the projects including SPP, SCP, DFE, and A/SP-IRG DOE NSP, participated by all major U.S. automotive OEMs and material suppliers.

Customer feedback and collaborations are paramount to LS-DYNA’s future. The experience shared by our customers is one of the driving forces for the advancements and improvements of our software.

Metal Forming Process Basics

The process below shows a typical draw development process of an automotive stamping from final finished product to the complete draw die faces.

There are many types of draw die process, as shown below:

From left to right, these different draw processes are explained below:

  • Air Draw
    • - Single action. 3-piece die system with 1 piece upper (cavity) and 2 piece (binder and punch) lower; upper cavity moves down.
  • Toggle Draw
    • - Double action. 3-piece die system with 2 piece upper (binder and punch) and 1 piece (cavity) lower; uppers moves down.
  • Air Draw with Pressure Pad
    • - Single action. Pressure pad added on top of regular air draw.
  • Stretch Draw (four piece)
    • - Double action. 4-piece die system with 2 piece upper (upper binder and cavity) and 2 piece lower (lower binder and cavity). Upper binder moves down to close with lower binder, moving together for a certain distance then upper cavity comes down to close with punch.
  • Crash Form
    • - Single action with no binder. Upper and lower tool takes the same shape and upper moves down.

One of the most important die processes includes trim and flanging dies (line dies). What happens in the trimming and flanging process often influence what needs to be done ahead in the draw development. Anticipating how sheet metal will flow in the downstream process requires years of stamping experiences. Simulation of the line die processes often helps avoid tens of thousands of dollars of draw die rework as a result of either wrinkling or split in the flanging process. The picture below shows typical flanging processes:

Die (structure) design begins as soon as product and process designs are completed. Shown below is a draw die design. Designs of other line dies, such as trim and flanging dies, etc. are included in this process.

At the same time as the draw die faces and line dies are designed, stamping sub-assembly process design is conducted. This type of process involves various types of hemming process, as shown below:

Metal Forming Related Keywords

The following links provide updated keyword manual pages related to metal forming; check back often for updates and additional new keywords.

Element Technology

The most used elements for sheet forming are of element type #2, and #16.

In-Plane Integration Point

Element Type #2 (Belytschko-Tsay shell), as shown above, features the following,

  • One in-plane integration point (reduced integrated shell)
  • Suitable for in-plane stretching
  • Suitable for thickness/thinning prediction
  • Ideal for forming application where no further springback simulation is desired
  • Defined with the variable ELFORM=2 in *SECTION_SHELL
  • Default element in LS-PrePost Metal Forming eZ-Setup in Levels 1 and 2 – for early feasibility and for formability only.

Element Type #16 (Belytschko-Tsay shell), as shown above, features the following,

  • Four in-plane integration points (fully integrated shell)
  • Suitable for non-uniform in-plane stress distribution
  • Suitable for bending & unbending producing non-uniform in-plane stresses
  • Ideal for situation where stress accuracy is more important
  • Ideal for forming simulation where ensuing springback simulation is desired, for line-die and hemming simulation, stoning, and for all implicit calculation
  • Costs slightly more CPU time compared to Element #2
  • Defined with ELFORM=16
  • Default in LS-PrePost Metal Forming Application GUI in Level 3 - for springback

Other elements include element types #25 (Belytschko-Tsay shell), and #26 (fully integrated shell) with thickness stretch.

Out-of-Plane Integration Point

Illustrated below, a type 16 element with 5 out-of-plane integration points is shown. The number of out-of_plane integration point is defined through the variable NIP in keyword *SECTION_SHELL.

The number of out-of-plane integration points (NIP) controls how accurately one can capture the through the shell thickness stress-strain information. Typical through the thickness stress patterns in metal forming are shown below:

Each of the cases represents the following,

  • Case I – a pure elastic bending distribution
  • Case II – elastic and plastic bending
  • Case III – bending with in-plane stretching
  • Case IV – distribution after springback

The following illustrates the consequences on the selection of NIP in capturing the stress distribution in the cases,

  • NIP=2 – causes no error for Case I; cause errors for Case II, III, IV
  • NIP=3 – no error for Case I; error for case II, III; big error for Case IV
  • NIP=5, or 7 – no error for Case I; small error for Case II, III, and IV.

Other frequently used elements in metal forming are various 3-D solid and 2-D elements. Solid elements are defined with the variable ELFORM in *SECTION_SOLID,

  • ELFORM=-2 – fully integrated S/R solid, for poor aspect ratio, accurate formulation
  • ELFORM=2 – fully integrated S/R solid
  • ELFORM=1 – constant stress solid element

2-D elements are defined with the variable ELFORM in *SECTION_SHELL,

  • ELFORM=12 – plane stress (explicit and implicit)
  • ELFORM=13 – plane strain (explicit and implicit)
  • ELFORM=14 – axisymmetric solid area weighted (explicit only)
  • ELFORM=15 – axisymmetric solid volume weighted (explicit and implicit)

Contact and Friction Modeling

Contact Types

The contact interfaces in metal forming are the FORMING types of contact:

  1. *CONTACT_FORMING_ONE_WAY_SURFACE_TO_SURFACE
  2. *CONTACT_FORMING_SURFACE_TO_SURFACE

Type ‘a’ is the most commonly used contact types in stamping simulation. Type ‘b’ treats both the blank and the rigid bodies equally, and it is slightly more time consuming. Type ‘b’ is needed in some cases where mesh density between blank and tools differ too much, and is also used frequently in implicit simulation.

There are some features specific and unique to the FORMING type of contact:

  • Regardless whatever thickness is specified in *SECTION_SHELL, the rigid bodies (tools) have no thickness;
  • Negative thickness offset using the variable MST in *CONTACT… for the tools is frequently and convenient used for upper/lower die thickness offset;
  • Disjoint/unconnected elements in tool meshes are allowed; LS-PrePost offers the best automatic tool meshing for forming simulation;
  • Sheet blank must be slave surface; tools must be master surfaces.
  • Mesh adaptivity works the best with Forming type contact; and a host of other features are developed specifically for Forming contact.

The contact thickness offset (virtual offset) can be selected in the eZ Setup in the first Setup page of the LS-PrePost Metal Forming Application GUI, as marked below. The amount of the tooling offset by default is 1.1 times blank thickness.

In LS-DYNA, draw bead is also modeled through contact, which will be discussed in the Draw Bead Modeling section.

Friction

The most common type of friction used for metal forming is the coulomb friction model. The default coefficient of friction (COF) in LS-PrePost is 0.12. This default value can be changed in the eZ Setup, under Control/Show.

A more advanced friction model is orientation dependent and pressure sensitive. This is done through the use of *DEFINE_FRICTION_ORIENTATION, where a detailed description is provided.

Material Model

LS-DYNA has over 200 types of material models available, with roughly the following models are related to sheet metal forming. Among the list below the first ten are the most frequently used:

  • MAT_037: MAT_TRANSVERSELY_ANISOTROPIC_ELASTIC_PLASTIC (1948 Hill’s anisotropy model)
  • MAT_036: MAT_3-PARAMETER_BARLAT (1989 Barlat’s model, aluminum)
  • MAT_133: MAT_BARLAT_YLD2000 (aluminum)
  • MAT_125: MAT_KINEMATIC_HARDENING_TRANSVERSLY_ANISOTROPIC (Yoshida non-linear kinematic hardening rule with M37)
  • MAT_226: MAT_KINEMATIC_HARDENING_BARLAT89 (Yoshida with M36, aluminum)
  • MAT_242: MAT_KINEMATIC_HARDENING_BARLAT2000 (Yoshida with M133, aluminum)
  • MAT_122: MAT_HILL_3R (1948 planar anisotropy w/ three R’s, Yoshida option)
  • MAT_020: MAT_RIGID (For rigid tools)
  • MAT_024: MAT_PIECEWISE_LINEAR_PLASTICITY (solids)
  • MAT_018: MAT_POWER_LAW_PLASTICITY
  • MAT_165: MAT_PLASTIC_NONLINEAR_KINEMATIC (Lemaitre & Chaboche)
  • MAT_136: MAT_CORUS_VEGTER (Vegter yield)
  • MAT_113: MAT_TRIP (For austenistic stainless TRIP steel)
  • MAT_106: MAT_ELASTIC_VISCOPLATIC_THERMAL
  • MAT_033_96: MAT_BARLAT_YLD96
  • MAT_190: MAT_FLD_3-PARAMETER_BARLAT
  • MAT_103_P: MAT_ANISOTROPIC_PLASTIC
  • MAT_244: MAT_UHS_STEEL

One of the new features LS-DYNA offers is the failure (necking) prediction of sheet metal under the non-linear strain path. Currently this capability is implemented in *MAT_036 and *MAT_037. The details are documented in the Metal Forming Related Keywords.

Adaptive Mesh Refinement and Fusion

Adaptive mesh refinement is a critical feature in metal forming. It helps in reducing the mass scaling induced inertia effect, especially for large, unsupported exterior panel stampings. It controls the number of elements by creating in locations where they are needed most. It is an important tool in increasing the computational efficiency. It should be used with caution, as increased number of mesh adaptive levels accumulates more adaptivity induced error, especially in forming for springback simulation.

The keyword is *CONTROL_ADAPTIVE. The ‘look-forward’ refinement option enables blank mesh refining starting at a user specified approaching distance to tooling. The levels of refinement, frequency of refinement, minimum element size allowed, and the angle criterion can be specified. In the eZ Setup, these variables are automatically set for the three levels and users have the option to modify each variable before job submission, as shown in the LS-PrePost Metal Forming Application .

Mesh fusion is also possible, and is done through the use of card #3 in the keyword. Shown below is an example of fusion on the NUMISHEET 2005 Cross Member, where the mesh refines first as the sheet blank goes through the draw die radius, then fuses together in the relatively flat area of the draw wall.

Specifying Mesh Fusion Criteria

 

Adaptive Mesh Refinement and Fusion on NUMISHEET’05 Cross Member

For localized forming and flanging, where meshes are deformed in specific local areas, the adaptive box can reduce number of elements and avoid unnecessary refinement in areas not needed. Detailed information can be found in *CONTROL_BOX_ADAPTIVE. The boxes are easy to create in LS-PrePost, through Model/Entity menu, as shown below.

Creation of Adaptive Box to Control Local Mesh Refinement

LS-PrePost Menu Access to Adaptive Box Creation

Draw Bead Modeling

There are two methods to model the draw beads, used to control the blank flow during forming.

Method 1 - Analytical line bead

  • Draw bead is defined by:
    • - a consecutive list of slave nodes, or,
      - beams
  • Plastic strain in sheet due to bending and unbending can be defined optionally
  • Equivalent restraining force is input and calculated based on the tensile strength
  • Recently developed feature automatically generates multiple line beads with equal amount of force divided among them, ideal for cases where the final sheet blank edge position is really close to the line bead
  • Advantage:
    • - less refined blank mesh in the bead region
      - faster computation efficiency
  • For Level 1 and some Level 2 (accurate) simulation; not for Level 3 simulation (see LS-PrePost Metal Forming Application)
  • Accessible through eZ Setup in LS-PrePost, under DrawBead menu.

Method 2 - Real draw bead

  • Draw bead shape is an integral part of the tools; very accurate
  • Fine mesh is needed in the draw bead area
  • Smaller time step is required (set DT2MS accordingly) to avoid dynamic effect
  • For Level 2 (accurate) and especially Level 3 (for springback/hard die release)
  • Draw bead shape/geometry can be determined precisely with this level of simulation and released for NC machining of the hard tools
  • Press tonnages prediction are more accurate

Real draw beads provide more accurate results. The 'pull-in' from the blank edge, and more importantly, the 'tightening' of the sheet blank within the punch opening during the bead closing can be more realistically simulated. In cases where portion of the finished part is designed on the binder for material utilization purpose, the skid, or impact marks can be vividly simulated, followed by a springback analysis to see how the marks affect the quality of the stampings. Some of LS-DYNA's metal forming users use only real beads for all hard die decisions, or at least for the major closure panels and deep-drawn parts. A comparison between restraining forces by real draw beads and test data is listed below:

Implicit Application

Implicit static algorithm is mostly applied in the gravity initialization of the blank, in binder closing, and in flanging simulation. Implicit technology has the unique advantage of the total absence from the inertia effect. This advantage is especially important in binder closing simulation of large exterior panel, where over 90% of the blank is unsupported in the die cavity; and in free flanging process, where large areas of the flange are just taking a free ride for the most part of the process, not going into contact (support) with the flanging steel until the last few millimeter of the travel. Dynamic inertia effect is most prominent in area of the unsupported blank in these processes. Implicit static technology in LS-DYNA offers a much more realistic simulation results in these situations.

With the advance of computer hardware and MPP technology within LS-DYNA, full-scaled industrial production parts can now be done in implicit static with very reasonable amount of turn-around time. With sufficient memory, SMP is efficient for models over 100,000 elements on the blank. For blank with over 100,000 elements, the name of the game is MPP.

The implicit static capability is offered through the use of the keyword *CONTROL_IMPLICIT_FORMING, where detailed usage is provided.

Springback and Compensation

Springback and compensation technology in LS-DYNA is the single most important tool responsible for millions of dollars in cost savings resulting from no or reduced number of die recuts. This powerful feature is battle hardened through vigorous industrial application and prove-out, and is available through the use of the following keywords, where all capabilities and many examples are provided:

*INTERFACE_COMPENSATION_NEW,
*INCLUDE_COMPENSATION_OPTIONS, and
*DEFINE_CURVE_COMPENSATION_CONSTRAINT_OPTIONS.

The main features of the iterative springback compensation technology in LS-DYNA include:

  • Displacement based. User set the compensation scale factor, usually between 0.7~1.0, unchanged throughout the iterative process.
  • Compensation amount is based on the factor and springback amount, in the opposite direction of the springback.
  • In the engineering stage of the dies, successful compensation hinges on the use of accurate springback prediction from LS-DYNA®,
    • Input: mesh after forming, mesh after springback, original tool mesh, bridge displacement;
    • Output: compensated tool mesh;
    • Process dependent - simulate the entire die process.
  • In later stage of hard die build, use of scan data makes accurate compensation possible.
  • "Alternated dual directional target approaching”: usually need 3~4 iterations to reach target (about +-0.5mm).

Global & Iterative Springback Compensation of Draw Dies

  • This is used where an entire part needs to be compensated. An example of such application can be found here.
  • Additionally, two important issues, "symmetric boundary condition", and "3-D trim curves mapping" must be addressed, as shown below:

Local & Iterative Springback Compensation of Draw Dies

  • This is used where one or more localized regions within a part needs to be compensated. The region(s) is defined by two enclosed curves. In addition to examples provided here, another example on the NUMISHEET 2005 decklid inner is shown below:

Compensation of Trim Dies

  • This is used where a (to be) trimmed part needs to be compensated. The need arises where additional springback has occurred between end of drawing and end of trimming, causing the trimmed panel not 'nesting' on the original trim post. The post is often compensated so when the trim pad comes down to push the drawn panel against the post the panel will not be moved out of position, resulting in bad trim lines. An example of such application can be found here.

Compensation of Flanging Dies

  • This is used where a flanging area needs to be compensated. An application example is shown below:

 

Application of Iterative Compensation in Later Stage of Die Construction

Your hard tool panels are hit, and analysis of the scan data reveals there is a need to compensate for dimensional deviation. This typically is caused by a late product change that was not captured during the Engineering stage, or by a change in die process, tooling, etc. LS-DYNA offers two methods to handle the situation. In this case, the springback panels used for the compensation input is exact, since the scanned STL file will be used as the tool to obtain the springback mesh.

  • “Push” with Implicit Static - An example can be found here.
  • "Crash" forming with Explicit Dynamic or Static Implicit - The scan data is used as rigid tools for the upper and lower dies to form the trim panel from baseline iteration "ITER0".

LS-PrePost® Metal Forming Application

LS-PrePost provides the most up-to-date support for metal forming features in LS-DYNA. This is accomplished through the “eZ Setup” GUI in the Metal Forming menu accessible through APPLICATION pull-down menu. The goal of the eZ Setup is to take the burden off the users in creating LS-DYNA input decks that utilize the latest features for sheet metal forming.

The eZ Setup is capable of setting up a typical entire stamping simulation process including gravity, binder closing, drawing, trimming and springback simulation, or any individual stamping process, or a combination of any processes, as shown in the figure below:

All necessary information is input through the GUI driven menu according to the process selected, and output into a set of files, used to submit to a LS-DYNA simulation. The CASE driver allows the user to submit a single simulation that consists of all the process defined. Furthermore, the color coded (yellow: to be defined; green: already defined) GUI system and the Next button make it difficult to miss any definition needed for the processes selected.

The eZ Setup also includes a material library covering the most common material types used for the simulation. The material files are located in the LS-PrePost installation directory, under a directory called lspp_matlib. The material specifications are readily identifiable from the file name.

The input files are fully parameterized through the use of a set of ASCII control files that are specific to the draw types, accuracy/speed levels desired. These control files are located in the LS-PrePost installation directory, under a directory called lspp_forming:

There are three forming control levels available in the eZ Setup, as seen in the following figure. These levels regulate the balance between accuracy and speed, for different simulation objectives:

  • Level 1 – for early feasibility
  • Level 2 – for formability only
  • Level 3 – for springback

Level 1 provides the fastest possible turn-around CPU time while maintaining the necessary overall accuracy; Level 2 provides detailed accuracy with fast CPU time; Level 3 uses all the bells and whistles necessary in the forming for the accurate springback prediction and compensation.

These levels are designed specifically each of the stated purpose, and the default variable definitions such as tool speed, mass scaling, adaptive refinement levels, etc., can be shown with the button Show, and modified, if needed, as shown below:

The following chart provides a performance comparison among the three levels:

The eZ Setup utilizes the latest automatic positioning feature and is capable of the following:

  1. Gravity loading with Implicit Static, pre-bending optional;
  2. Implicit static binder closing for both air and toggle;
  3. Three-piece air and toggle draw;
  4. Trimming in both 2-D and 3-D;
  5. Springback simulation with implicit static;

Examples and Verification

  1. NUMISHEET 2001 BM4

  2. Formability Index (F.I.) for *MAT_037

    An example below shows an area of a stamping with highly non-linear strain paths, resulting in a safe prediction when plotting with a traditional FLD curve. Plotted using the Formability Index, it actually already reached the necking limit.

  3. *MAT_125(*MAT_KINEMATIC_HARDENING_TRANSVERSELY_ANISOTROPIC)
  4. *MAT_226 (*MAT_KINEMATIC_HARDENING_BARLAT89)

    Testing results on a single element in various cyclic loading conditions are shown below.

    Single Element Testing – Multi-cycle Uniaxial Tension/Compression

    Single Element Testing – Multi-cycle Biaxial Tension/Compression

    Single Element Testing – Multi-cycle Shear

    Single Element Testing – Multi-cycle Plane Strain

    An industrial example shown on a hood inner indicates under the same draw bead condition, *MAT_226 results in more localized thinning in plane strain condition than in *MAT_125. Wrinkling conditions are more severe in *MAT_226 than in *MAT_125.

    *MAT_125 on a Hood Inner (Courtesy of Ford Motor Company Research and Engineering Laboratory)

    *MAT_226 on a Hood Inner (Courtesy of Ford Motor Company Research and Engineering Laboratory)

  5. Constraint-free Springback Prediction with Inertia Relief

    This unique feature allows for a constraint-free springback simulation, preferred in many tool and die shops. All rigid body modes are removed within the solver automatically to avoid singularity. Typically, a two-step process is needed.

    1. First, in the usual springback simulation run, boundary conditions are removed. The following keyword is added to extract seven eigenvalues from the structure:
        *CONTROL_IMPLICIT_EIGENVALUE
        $NEIG
        7
    2. Second, when eigenvalue simulation is completed, d3eig file is read into LS-PrePost for viewing of eigenvalues and eigenvectors. A threshold frequency is selected as a value between the 6th and 7th eigenvalues, and set as the variable THRESH(=0.02 below) in the following keyword:
        *CONTROL_IMPLICIT_INERTIA_RELIEF
        $IRFLAG THRESH
        1, 0.02

    Since the first six modes are typically small and the 7th mode is a few orders larger than the 6th mode, it is possible to skip the first step all together, and use the fixed value of 0.02 for all THRESH. The following example shows the technique of inertia relief used on NUMISHEET 2002 Fender Outer. It is recommended to use the DYNAIN file generated by LS-DYNA run of a previous process.

  6. Linear Static Analysis on Structures

    Linear static simulation can be applied on die structure analysis. It is typically used to determine if the die is under the fatigue limit and if it meets the deflection requirement under various loads. It can also be used to optimize the die structure for lean die manufacturing. The following provides a validation of a cantilever beam modeled with both shells and solid elements:

  7. Denting Analysis

    One of the application area of the implicit capability is the static denting simulation. An sphere-shaped indenter is applied with Force or Displacement, with single or multiple cycles, to be pushed against a panel to be studied. Dent depth on the panel is studied after the indenter is withdrawn. The following shows denting simulation results, based on the model from SAE paper 2002-01-0789.

AVI Library

  1. Deep drawing (toggle), trimming, multiple flanging simulation of a boxside outer panel – courtesy of Autodie LLC.

  2. Scrap trimming and shedding simulation of a trim die involving by-pass and aerial cams – courtesy of Ford Motor Company.

  3. Implicit binder closing in air – NUMISHEET’02 fender outer.

  4. Implicit binder closing in toggle – NUMISHEET’05 decklid inner.

  5. Implicit flanging simulation - NUMISHEET’02 fender outer.